As is known in the art, there are various means for monitoring indoor environmental or air quality parameters. One approach involves the use of facility monitoring systems or also referred to as multipoint air monitoring systems. In the context of this invention a multipoint air monitoring system is defined as a monitoring system that includes at least one environmental or air quality parameter sensor that measures at least one air quality parameter for a plurality of rooms, spaces, areas, air ducts, or environments within a building or the ambient conditions surrounding or adjacent to a building or facility. As such a multipoint air monitoring system may involve the use of one or more individual, local, wired or wireless sensors located in the space or area being measured. It may also use remote or centralized air quality parameter sensors that are multiplexed or shared amongst a plurality of spaces as is described in more detail later. Finally, a multipoint air monitoring system may use a combination of the previously mentioned remote and local air quality parameter sensors.
Typically, many of these facilities where multipoint air monitoring systems will be employed involve the use of air handling units that involve return air where a percentage of the air returned to the air handling unit is mixed with some percentage of outside air to provide supply air to various rooms or spaces within a building. Alternatively, the building may in some cases contain critical environments such as laboratories or vivariums which are one pass environments that do not use return air and instead exhaust all the air supplied into the critical environment rooms. Although many of the figures of this patent are directed to a building with return air, the invention can also be used for one pass critical environments as well. A related U.S. patent application that involves the use of multipoint air monitoring systems and the blending of air quality parameter sensor signals for dilution ventilation control applications within one-pass critical environments is titled “Dynamic Control Of Dilution Ventilation In One-Pass, Critical Environments” by Sharp and Desrochers and was filed on Mar. 10, 2006 concurrent with this application and is incorporated herein by reference.
For those multipoint air monitoring systems where remote sensors are used, air is transported through a tube or pipe for sampling or measurement purposes. For example, a multipoint air monitoring system may have one or more centrally located air quality parameter sensors instead of distributed sensors local to the sensed environment. As such, this centralized air quality parameter sensor may be used in these systems to sense several or a large number of locations. These centralized air monitoring systems are also referred to in the context of this invention as multipoint air sampling systems, or as multiplexed or shared sensor based facility monitoring systems.
Multipoint air sampling systems are defined for the purposes of this invention as specifically a facility monitoring system that uses shared or multiplexed sensor(s) consisting of either a single remote sensor or a set of remotely located sensors that is used to monitor a plurality of spaces, areas or rooms within a building, or outside adjacent to a facility by transporting samples or packets of air from the spaces to be monitored to the at least one air quality parameter sensor.
For one class of these multipoint air sampling systems specifically defined, in the context of this invention, as star configured multipoint air sampling systems or just star configured systems, multiple tubes may be used to bring air samples from multiple locations to a centralized sensor(s). Centrally located air switches and/or solenoid valves may be used in this approach to sequentially switch the air from these locations through the different tubes to the sensor to measure the air from the multiple remote locations. Each location may be sensed for between 10 seconds or several minutes. Depending on how many locations are sensed each space may be sensed on a periodic basis that could range from 5 to 60 minutes. These star configured systems are sometimes called octopus-like systems or home run systems and may use considerable amounts of tubing.
Systems such as this, for example, have been used to provide monitoring functions for the detection of refrigerant leaks, and other toxic gas monitoring applications. Other systems similar to this, such as that described within U.S. Pat. No. 6,241,950 to Veelenturf et al., which is incorporated herein by reference, discloses a fluid sampling system including a manifold having inputs, common purge and sampling pathways, and valves to couple/decouple first and second sets of inputs for measuring pressure differentials across sample locations.
Additionally, these types of star configured systems have been used to monitor particulates in multiple areas such as clean room areas with a single particle counter. A prior art example of this is a multiplexed particle counter such as the Universal Manifold System and Controller as made by Lighthouse Worldwide Solutions, Inc. coupled with one of their particle counters such as their model number Solair 3100 portable laser based particle counter or an obscuration based particle sensor.
Regarding absolute moisture or dewpoint temperature measurement an example of a prior art star configured multipoint air sampling system that can be used to measure dewpoint temperature is the AIRxpert 7000 Multi-sensor, Multipoint Monitoring system manufactured by AIRxpert Systems of Lexington, Mass., www.airexpert.com.
Another multipoint air sampling system defined in the context of this invention as a networked air sampling system uses a central “backbone” tube with branches extending to various locations forming a bus-configured or tree like approach similar to the configuration of a data network. Air solenoids are typically remotely located proximate to the multiple sampling locations. The sampling time for each location like with the star configured systems may vary from about 10 seconds to as much as several minutes. A typical sampling time per location would be about 30 seconds, so that with 30 locations sampled, each location could be sampled every 15 minutes. Networked air sampling systems can potentially be used to sample locations within a building, an air handling unit ductwork, exhaust air stacks of a building, or outside a building. An exemplary networked air sampling system is described in U.S. Pat. No. 6,125,710 to Sharp, which is incorporated herein by reference. U.S. patent application Ser. No. 09/779,379 to Sharp et. al., titled “Air Quality Monitoring Systems and Methods”, references different multipoint air monitoring systems including multipoint air sampling systems as used with expert system analysis capabilities and is also incorporated herein by reference.
Finally another multiplexed form of facility monitoring system that may be used to implement portions of this invention is defined in the context of this invention as a networked photonic sampling system that multiplexes packets of light vs. packets of air and may incorporate either a star configured or network/bus type of layout. The basic concept uses a central laser emitter and a central laser detector that sends out and detects laser light packets that are switched into rooms to be sensed by optical switches. Optical fiber sensors, infrared absorption cells or sensors, and other sensing techniques are located and used in the sensed area to change the properties of the light due to the affect of the environment. The light packet is then switched back to the central detector where the effect of the environment on the light properties is determined. A major benefit of the system is that the sensors such as the fiber or open cell sensors are potentially quite low in cost. The expensive part is the laser and detector systems that are centralized. Similar to the previous multipoint air sampling systems, multiple affects on the light from particles, gases and other contaminants, humidity, etc. can be done simultaneously with central equipment and the telecom concept of Wavelength Division Multiplexing which allows multiple wavelengths and hence multiple signals to share the same fiber. A clear advantage of this system is the ability to have a very rapid cycle time that can be in the ten's of milliseconds or less. This sampling system is detailed in U.S. Pat. No. 6,252,689, entitled “Networked Photonic Distribution System for Sensing Ambient Conditions” and is incorporated herein by reference.
The multipoint air sampling systems and networked photonic sampling system which have been described heretofore and are collectively referred to as sampling systems may be applied to monitor a wide range of locations throughout a building, including any kinds of rooms, hallways, lobbies, interstitial spaces, penthouses, outdoor locations, and any number of locations within ductwork, plenums, and air handlers. To provide control as well as monitoring of these different spaces, virtual sensor signals can be created that in the context of this invention refer to software or firmware variables, or continuous analog or digital signals that can be passed to other systems such as a building control or laboratory airflow control system and are representative of the state of a given space's air quality parameter value. In effect these signals are reflective of what a local sensor would read if it was being used instead of the multipoint air sampling system or networked photonic sampling system otherwise known collectively again as sampling systems.
Multipoint air sampling systems have been used with a wide variety of air quality parameter sensors to monitor a wide variety of air quality attributes or air characteristics of a building or facility. In the context of this invention an air quality parameter sensor is a sensor that can detect one or more air quality attributes or parameters that convert the level of or information about the presence of an air quality parameter into either a continuously varying or else discontinuous pneumatic, electronic, analog or digital signal or else into a software or firmware variable representing the level of or information about the presence of an air quality parameter in a given space. The air quality parameter sensor may be based on any of a variety of sensing technologies known to those skilled in the art such as for example electrochemical, photonic or optical, infrared absorption, photo-acoustic, polymer, variable conductivity, flame ionization, photo-ionization, solid state, mixed metal oxide, ion mobility, surface acoustic wave, or fiber optic. The air quality parameter sensor may be a wired or wireless sensor type and be implemented with various types of physical hardware such as for example micro-electro-mechanical system based (MEMS), nanotechnology based, micro-system based, analog based, or digital based. Additionally, an air quality parameter sensor may sense for more than one air quality parameter, and may include more than one air quality parameter sensor in a single packaged device.
Furthermore, for the purposes of this patent an air quality parameter is defined as an air characteristic that can consist of an air contaminant, an air comfort parameter, or carbon dioxide (CO2). An air contaminant in the context of this patent refers to certain potentially harmful or irritating chemical, biological, or radiological composition elements or properties of the air such as for example CO, particles of various sizes, smoke, aerosols, TVOC's (Total Volatile Organic Compounds), specific VOC's of interest, formaldehyde, NO, NOX, SOX, SO2, hydrogen sulfide, chlorine, nitrous oxide, methane, hydrocarbons, ammonia, refrigerant gases, radon, ozone, radiation, biological and or chemical terrorist agents, other toxic gases, mold, other biologicals, and other contaminants of interest to be sensed. An air contaminant specifically does not refer to such other air quality parameters such as temperature, carbon dioxide, or any one of the many forms of measuring moisture or humidity in air such as for example relative humidity, dewpoint temperature, absolute humidity, wet bulb temperature, enthalpy, etc.
Furthermore, air contaminants can be further subdivided into two categories, gas based contaminants and particle based contaminants. Gas based contaminants are defined in the context of this invention as air contaminants that are gas or vapor based such as CO, TVOC's, ozone, etc. Particle based contaminants on the other hand consist of viable and nonviable air borne particulate matter of any size, but generally of a particle size from 0.01 microns up to 100 microns in diameter. As such this category of contaminants also includes all biological particulate matter such as mold spores, bacteria, viruses, etc.
Carbon dioxide refers specifically to the gas carbon dioxide that is found naturally in the atmosphere as a component constituent in addition to oxygen and nitrogen. It is typically found in outside air at concentrations between 300 and 500 PPM and is exhaled by human beings at an approximate rate of 0.01 CFM per person for a person doing typical office work. Variations in the number of people in an office compared to the amount of outside air supplied into the building can easily vary indoor CO2 levels to between 500 and 2500 PPM. As such CO2 can be used as an excellent indicator of proper ventilation on a per person basis sometimes referred to as the CFM of outside air per person since the level of CO2 in a space is directly related to the number of people in a space divided by the rise in CO2 from outdoor levels. Although high CO2 levels are often associated with poor indoor air quality levels, it is not the level of CO2 itself that creates the discomfort and symptoms associated with poor indoor air quality but instead the associated rise in air contaminants that are not being properly diluted. Human beings are unaffected by relatively high levels of CO2 such as up to 5000 PPM, which would be extremely rare to find in any building of ordinary construction.
For the purposes of this patent an air comfort parameter specifically refers to either the measurement of temperature or one of the many related psychrometric measurements of moisture or humidity in air such as again, relative humidity, dewpoint temperature, absolute humidity, wet bulb temperature, and enthalpy. An air comfort parameter also does not refer to either carbon dioxide or any air contaminants. Additionally, in the context of this invention, an air quality parameter, air contaminant, or air comfort parameter specifically do not include any measure of airflow volume, velocity or pressure such as for example measurements of air volume that may be indicated in units of cubic feet per minute of air or other units, velocity pressure, air speed or velocity, static pressure, differential pressure, or absolute pressure.
In the past, prior art multipoint air sampling systems have been used from time to time to provide monitoring, data logging, alarming, control, or limit functions for one or more individually sensed air quality parameters but not for blended or composite air quality parameter signals.
In the context of this invention, a blended air quality parameter signal, also referred to as a composite air quality parameter signal, is defined as an analog signal, digital signal, optical signal, software or firmware variable or address location or other time based representation of information that is affected by, related to, or in some manner a function of a plurality of air quality parameters relating to one or more locations such as rooms, spaces, areas, air ducts, or critical environments within a building or the ambient conditions surrounding or adjacent to a building or facility. Such a blended or composite air quality parameter signal can be used to realize benefits such as simplicity, accuracy, cost effectiveness, and reliability compared to prior art approaches. The blended signals can also uniquely enable new air flow control applications as described later, as well as be used for general IEQ monitoring, commanding airflow control devices, or used in the control of any aspect of a building's operation to which they are pertinent such in conjunction with its HVAC and building controls system.
Concerning other aspects of the prior art, the alarm or limit function output signals for individual air quality parameters from multipoint air sampling systems have in the past sometimes been communicated to other systems, such as a building management system (BMS) which, based on the state of these functions, can affect aspects of the operation of a building, such as for example the air flow rate to a location within a zone monitored by the multipoint air sampling system in which the monitoring system has detected that an individually sensed air quality parameter has exceeded a predetermined limit. For example, sampling based refrigerant monitoring systems are examples of multipoint air sampling systems that provide alarm/limit functions such as this for individual parameters in which one or more relay contacts or analog output signals (such as 0-10 volt or 4-20 milliamp signals) are provided either locally where the shared sensor or sensors reside or via remote modules that are in communication with the sensor hardware via a digital network. The VASQN8X multipoint refrigerant monitor by the Vulcain division of BW Technologies, is an example of a monitoring system with capabilities such as this. In this way, multipoint air sampling systems have been used to provide a discontinuous signal, typically via a relay contact, which in turn provides a discontinuous control function based on a single air quality parameter. Note that in the context of this patent a discontinuous signal is defined as one with a limited set of values or states such as two or three states and steps between the values with no intermediate values or states. A discontinuous control function in the context of this patent is similarly defined as one with a limited set of output values or states such as two or three and similarly steps between these values with no intermediate values or states.
U.S. Pat. Nos. 5,292,280 and 5,267,897 describe another multipoint air sampling system that monitors a single trace gas, typically carbon dioxide (CO2), at multiple locations, including return air, outside air, and the supply discharge air associated with an air handler in order to directly compute the outside air flow component for purposes of controlling the air handler. This method uses a common CO2 or trace gas sensor and valves assigned to each of the sampled locations to provide a multiplexed signal from the CO2 sensor that varies in time based on the current location being sampled. The time variant signal from the shared CO2 sensor is read by a separate control module, where it is decomposed into three separate CO2 or trace gas signals, based on continuous knowledge of the sequence state, representing outside air, return air, and supply discharge air CO2 concentrations.
A similar multipoint air sampling system prior art method described by Warden in a paper entitled “Supply air CO2 Control of minimum outside air for multiple space systems”, David Warden, published in October of 2004 in the ASHRAE Journal applies a common single parameter CO2 sensor, using a three-way valve or two separate two-way valves to alternately switch air samples taken from an air handler's supply discharge air as well as that from outdoors. This creates a multiplexed signal that can be decomposed by a computer in the form potentially of a Direct Digital Control module (or DDC controller) in order to get a reading of supply air CO2 concentration with respect to outside air CO2 concentration that in turn can be used to control the outside air intake to the air handler.
U.S. Pat. Nos. 6,609,967 and 6,790,136 to Sharp and Desrochers discloses methods and apparatus to safely re-circulate air in a controlled ventilated environment for minimizing ventilation and thermal load requirements for each room, and thereby reducing the amount of required outside air. In particular, if one or more individual air contaminants are sensed in one of the rooms of the ventilated environment, the amount of air re-circulated from that room is reduced or potentially shut off to prevent contaminating other rooms in the ventilated environment.
Other prior art systems such as the AIRxpert 7000 Multi-sensor, Multipoint Monitoring system mentioned above or the networked air sampling system previously mentioned in U.S. Pat. No. 6,125,710 to Sharp discuss measuring multiple individual air quality parameters but again do not discuss how to create or employ a blended air quality parameter signal from these systems.
Additionally, heretofore the use of multiple individual local sensors to create composite signals from multiple locations would have involved a large number of individual sensors used with a building management system (BMS) or data acquisition system with an associated large first cost and large ongoing calibration costs. Multipoint air sampling systems on the other hand can sense multiple parameters cost effectively on a discrete sampled and individual basis, although as mentioned above, means has been lacking heretofore to properly combine and blend this information on a discontinuous or continuous basis so it can be beneficially applied to appropriate monitoring or control applications.
One pertinent application where blended air quality parameter information can be used to significant advantage involves room or area based demand control ventilation (DCV) as applied for example to an office, classroom, assembly, auditorium or variable occupancy space or air handling unit based demand control ventilation as applied to air handler of a building. As described in the previously mentioned paper by Warden entitled “Supply air CO2 Control of minimum outside air for multiple space systems”, the outside air into a facility as well as the amount of supply air into a given room or area can be varied based on the amount of people in the facility or the given area or room by measuring a proxy measurement for occupancy and ventilation which is CO2. As described previously, the more people in the space or building the more CO2 rises allowing a measurement of CO2 to drive and increase outside air into the building when the number of people increases or conversely allows the amount of outside air to drop when less people are in the space. Similarly for room or area based demand control ventilation when the CO2 level of an area rises, the supply air into the space can be increased to increase the amount of dilution ventilation in that space and conversely when CO2 levels drop due to a reduction in people in the space such as a conference room, the supply air into the space can be decreased down to the minimum supply air required to handle the room's thermal load to save energy.
Although these two demand control ventilation approaches of room based dilution ventilation control and air handler based outside air control has been used for some number of years, a problem with these concepts is the potential presence of non-human pollutants such as particles, carbon monoxide, TVOC's (Total Volatile Organic Compounds) or other air contaminants that can accumulate and rise in value when a source of them is present and ventilation levels are low. If for example a space is sparsely populated, and some strong and potentially irritating cleaning compounds are used in the space, problems could ensue for those existing occupants since the low level of occupants would have driven the ventilation rates down to a low level when in reality the presence of the cleaning compounds should necessitate a much higher ventilation rate. As mentioned in an ASHRAE Journal article dated July of 2003 titled “Demand Control Ventilation” by authors, Kurt W. Roth, John Dieckmann, and James Brodrick that although “In practice DCV has reduced annual energy costs by $0.05 to $1 per square foot . . . . Currently, most buildings do not use DCV because of concerns about nonhuman indoor pollutants mentioned previously.”
In addition to the previously high cost of sensing these non human indoor pollutants or air quality parameters it has also not been known to those skilled in the art of ventilation control how very different air contaminants such as TVOC's, particles, carbon monoxide and others should be used in conjunction with carbon dioxide information, which is itself not a contaminant, to properly control the outside air into the building through blending the elements of both demand control ventilation using CO2 plus dilution ventilation control based on one or more air contaminants.
Referring to another industry problem, although there are many advantages to solely using multipoint air sampling systems as described above to create a composite or blended air quality parameter signal, there are certain air quality attributes that can not be properly detected with the use of at least some if not all of these multipoint air sampling systems. Most notably, temperature can not be sensed remotely with a centralized sensor since the temperature of the air sample pulled through the air sampling conduit or tube will rapidly change temperature to equal the temperature of the sampling conduit or tube. In many cases the air does not need to travel more than 10 to 20 feet before its temperature has been substantially affected by the temperature of the sampling tubing. Furthermore, there are also other air quality attributes such as ozone or particles that depending on the type of tubing used or the speed of transport, may be affected by transport through the tubing.
With respect to temperature, for example, the inability of a remote sensor based multipoint air sampling system to measure the room or duct temperature at air sampling locations creates a problem in measuring such moisture related properties as relative humidity and enthalpy using a multipoint air sampling system. This is because only the absolute humidity, the amount of water vapor in the air in parts per thousand or the dewpoint temperature can be measured directly by a multipoint air sampling system. Thus, the difficulty in obtaining a measurement of the air sample's temperature before it is affected by the air sampling tubing and then combining or blending that temperature measurement with the absolute humidity measurement has in the past prevented the use of these multipoint air sampling systems for the monitoring or control in rooms or in air ducts of the blended air quality parameters of relative humidity and enthalpy.
This is potentially important since local relative humidity and enthalpy sensors, potentially used in the economizer of an air handling unit, are difficult to maintain and keep accurate when used as local sensors particularly for certain applications involving the measurement of outside air due to the wide ranging temperature of this air and it's typically heavy concentration of particulates and dust. For example, a recent study by the New Buildings Institute of economizers and air handling units in the Pacific Northwest stated that approximately two thirds of the economizers evaluated were not working properly or had failed completely in many cases due to the failure of the sensors.
To explain this application in more detail, an economizer as defined in the context of this patent is a system that exists as a part of a building air handling system for reducing cooling costs by introducing outside air in lieu of, or to assist with, mechanical cooling such as mechanical equipment based air conditioning. The effectiveness of an economizer is largely based on its ability to sense when outside air conditions are suitable so that the outside air can be used for so-called “free cooling” to reduce compressor use. U.S. Pat. Nos. 4,182,180 and 4,570,448, which are incorporated herein by reference, disclose exemplary techniques for using outside air for cooling. This includes dry-bulb temperature, single enthalpy, and differential enthalpy based economizers. Of these types of economizers, enthalpy based types (particularly differential enthalpy based economizers) have demonstrated better performance, especially in hotter more humid climates, where the latent heat load associated with cooling outside air can be a significant factor. For this application, enthalpy sensors are available for use with economizers such as Honeywell Part No. C7650, solid state economizer control.
Although the savings potential with enthalpy based economizers can be significant, these systems as mentioned above, often realize limited savings in practice due in part to issues with unreliable sensor technology, as is well known in the art. ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) has commented on the limited reliability of these sensors such as in the ASHRAE Standard 90.1 Users Manual. Known enthalpy sensors were based on a plastic filament that could deteriorate over time leading to failure or gross calibration errors. Newer sensors are based on solid-state designs, but they are still subject to drift and repeatability problems.
Centralized remote absolute humidity and chilled minor hygrometers are much more accurate, reliable and cost effective when used as part of a multipoint air sampling system. If the aspect of local temperature measurement could be cost effectively solved then these sensors could be advantageously used for the more commonly used measurements of relative humidity and enthalpy.
Another problem with economizers is that there are times when outdoor conditions are worse than indoor conditions such as with a building located near a major highway during rush hours. During these periods if the economizer is calling for free cooling, potentially 100% outside air is being drawn into the building which may be saving energy, but due to the high traffic outside the building the indoor air quality of the facility may actually be made worse. As a result it would be helpful to be able to create a blended outdoor air contaminants signal incorporating multiple air contaminants such as TVOC's, CO, and potentially particles that could be used with the air handler to override the economizer's control of outside air when the outside air is “dirty”.
One known problem with dilution ventilation in buildings using air contaminant sensors such as for example sensors for particles, CO, TVOC's or other air contaminants is that if the outside air concentrations becomes high enough, increasing the airflow volume of outside air or the supply air into a controlled area or room will actually increase the sensed air contaminant levels in a space, duct or air handler. This can potentially create a negative feedback situation when the inside dilution ventilation threshold levels are exceeded forcing the outside airflow levels and or room supply air flow levels to their maximum level. Depending on the level of design capacity of the HVAC system, the capacity of the air handling system could be exceeded in this latch-up situation, causing a degradation of HVAC system control.